The overall objective of this project is to determine the ability of newly available Doppler ultrasonic instrumentation to non-invasively detect and quantitate the various types of atherosclerotic plaques. The instrumentation to be applied includes the Infinite Gate Pulse Doppler, the Dual Directional C-W Doppler, the Doppler Velocity Readout and the two types of spectral analyzers. The specific aims are: 1) to evaluate the Infinite Gate Pulse Doppler in quantitating the lumen diameter and blood flow in the carotids, 2) to evaluate the mean velocity analogue readout in quantitating carotid artery stenosis, 3) to evaluate the dual directional Doppler in non-obstructing plaques and 4) to construct and clinically apply a low cost "comb-type" spectral analyzer in carotid evaluation. These aims will be met by performance of eight project tasks including: 1) construction of a "comb-type" spectral analyzer, 2) the construction and the use of a high resolution audio spectral analyzer, 3) quantitation of the carotid stenosis as compared with x-ray angiography, 4) the detection of minor degrees of turbulence with the dual directional flowmeter which might represent non-obstructive or obstructive plaques, 5) the clinical detection of non-obstructive plaques, 6) the separation of phase reversal produced by ultrasonic scattering in non-distorting plaques from phase reversal produced by turbulence, 7) carotid diameter measurement capability of the IGPD and 8) calculation from the IGPD output to measure volumetric blood flow.